When performing underground excavation, such as for example coal mining operations, it is desirable for efficiency purposes to continuously operate the mining apparatus breaking coal away from the face. In order to do so, means must be available for quickly and continuously hauling the loosened material from the mining site to an area removed from the mining site.
One such continuous haulage system presently available and used in coal mines comprises a series of conveyor mechanisms pivotally linked together. The components of this system wind there way through the mine from a continuous miner which breaks up the solid coal deposits to material sized to be more easily transported to an area distal therefrom. Some of the components which comprise these systems may be self-propelled mobile conveyor units while others may be conveyors which span or bridge an area between mobile units. The mobile units used in the continuous haulage system are sometimes referred to as mobile bridge carriers and are generally crawler mounted chain conveyor units.
In a continuous haulage system which may include, for example, several mobile bridge carriers, the first of the several mobile bridge carriers is positioned adjacent to the discharge end of a continuous miner. The mobile bridge carrier moves in concert with the continuous miner and accepts the mined material in a small hopper at its receiving end. Alternatively, a Feeder breaker may be positioned between the continuous miner and the mobile bridge carrier to break up the larger pieces of mined material. The discharge end of the mobile bridge carrier is pivotally connected to another continuous haulage system component, generally a bridge conveyor. A series of pivotally connected mobile bridge carriers and bridge conveyors provide the means to articulate the continuous haulage system around comers and allows it to move in concert with the continuous miner. The continuous haulage system thus provides a quick and efficient means for transporting the mined material from the face.
The pivotal connections between the various components of the continuous haulage system are generally provided by a yoke assembly including cooperating male and female portions. The yoke assembly, in the past, has been welded in a predetermined fixed position on the ends of the various components of the continuous haulage system. While welding yoke assemblies to the components does provide considerable structural strength which is necessary in the rugged environment of an underground excavation site, welding yoke assemblies also poses some considerable drawbacks.
The environment in which these continuous haulage systems are used may include seams in an underground excavation that may be as low as 32 inches high. One problem with welding the yoke assemblies in a fixed position, particularly when the continuous haulage system is maneuvered in a mine environment where the floor has undulations or rough spots, is that adjacent ends of the series of pivotally connected components have a tendency to interfere with each other. Additionally, seam heights in underground excavations are not consistent. Thus, in order to allow the system to be moved through a seam in concert with the continuous miner, the height of the yoke assembly connecting the various components is generally selected and welded at its lowest height so that it is movable through a seam of a low height. However, setting the yoke at a low level does not address the problem of interference between components. Furthermore, setting the yoke assembly at its lowest height limits the flow of material through the conveyor. Thus, if the continuous haulage system were being used in a seam which would permit the yoke assembly to be raised, running the system with the yoke assembly at its lowest height severely reduces the efficiency of the operation. Adjusting a welded yoke assembly is no easy task, and in order to raise a welded yoke assembly to a higher level when the seam height will allow such adjustment the welded yokes would have to be severed and rewelded generally requiring several days work.